Contamination from the metals lead, nickel, copper, zinc and cadmium may harm organisms at low concentrations if the metal compounds are in a bioavailable form, but they rarely cause ecological effects through biomagnification.
Copper in the Great Lakes
Most metals such as copper, zinc and iron concentrate in depositional sediments draining urban watersheds and also in areas where mining activities have occurred. In the Great Lakes, the highest copper concentrations are found in Lake Superior, just offshore of the Keweenaw Peninsula, an area of prevalent historic copper mining. More than 500 million tons of copper mine tailings were dumped into Lake Superior and its tributaries between 1895 and 1968.1
Effects of Exposure to Copper
- Copper’s bioavailability and toxicity to aquatic organisms can vary depending on the water body. It tends to be more toxic (more bioavailable) in water bodies that are low in dissolved minerals or organic matter, such as Lake Superior and its tributaries.
- Aquatic organisms typically accumulate copper through their food. Bottom-feeding invertebrates exhibit the highest concentrations of copper.
- Copper can be highly toxic at low concentrations to invertebrates and to fish in early life stages and can result in food web disruption.2
Mapping copper as a Great Lakes stressor
We mapped surficial sediment copper concentration from two data sources:
1. Near-shore data points were obtained from collection of monitoring and restoration projects.3
2. In-lake data values were provided by Environment Canada.4
Data were kriged using ArcGIS algorithms with a 5-point neighborhood. Point values ranged from zero to 308 ppm, and were highest around Upper Michigan’s Keweenaw Peninsula.
Spatial distribution of copper as a stressor in the Laurentian Great Lakes (Inset: Western Lake Ontario).
2. Brix K.V., D.K. DeForest, and W.J. Adams. 2011. The sensitivity of aquatic insects to divalent metals: A comparative analysis of laboratory and field data. Science of the Total Environment, 409(20):4187-4197.
3. NOAA Assessment and Restoration Division. 2011. National Sediment Inventory – Great Lakes watershed. Online: http://response.restoration.noaa.gov/watersheddownloads. Accessed 29 May 2011.
4. Marvin, C., S. Painter, D. Williams, V. Richardson, R. Rossmann, and P. Van Hoof. 2004. Spatial and temporal trends in surface water and sediment contamination in the Laurentian Great Lakes. Environmental Pollution,129:131-144.